The invention provides a 3D printer. The 3D printer comprises multiple printing machine heads, a travelling rail and a printing rack, wherein a ring-shaped rail is arranged on the travelling rail; a hollow structure is arranged in the ring-shaped rail; the travelling rail is fixedly arranged on the top of the printing rack through travelling rail pedestals; a hollow-out structure is arranged on the top of the printing rack; the hollow structure passes through the travelling rail pedestals and the hollow-out structure, and communicates with the inner part of the printing rack to form a printingcavity; and the printing machine heads are arranged on the ring-shaped rail, and can move along the ring-shaped rail for printing materials in the printing cavity. With the adoption of the scheme provided by the invention, needed time for printing components can be greatly reduced, and production efficiency of the equipment printing components is improved, so that the purposes of being energy-saving and environmentally-friendly, green and efficient are achieved.